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101 T HE ROOTS OF the human family go back some seven million years, or maybe a bit more. The order Primates to which we belong is first documented around the time the dinosaurs became extinct, some sixty-five million years ago, though early representatives might already have been around for some time. The first known mammal relative lived back in the Carboniferous, well over three hundred million years ago. In contrast, we human beings are mere parvenus. The fossil record and molecular comparisons agree that the human species is of remarkably recent origin and that it dispersed worldwide even more recently. Viewed in evolutionary perspective, those features that we recognize as “racial” were acquired only yesterday, mere seconds before midnight on the evolutionary clock, as it were; and what’s more, unlike furry skin, grasping hands, or upright posture, as intraspecific variations they are entirely epiphenomenal. In this chapter we will attempt to put them in historical perspective by briefly looking at the evolutionary history of the human family and at that fleeting moment in time that witnessed the origin and spread of Homo sapiens. As documented by fossils (principally the petrified bones and teeth of ancient animals preserved in sedimentary rocks), the story of our zoological family Hominidae (which you will often see alternatively classified as the subfamily Homininae; it’s of no consequence here) goes back to almost seven million years ago. This was the time around which the first creatures emerged that were more closely related to Homo sapiens than to any of the apes. The earliest known hominids, all of which date to the period between about seven and four million years ago, come from sites in Africa—and they make up a pretty motley bunch. What all mainly have in common is the claim, made by their describers for a variety of different reasons, that each was an upright biped, HUMANEVOLUTIONANDDISPERSAL CHAPTER 3 102 CHAPTER 3 walking on two legs when on the ground—where it seems they actually didn’t spend all, or even most, of the time. Descended from arboreal ancestors, the early hominids appear to have lived at a moment when drying and increased seasonality of the African climate was beginning to shrink the continent’s formerly monolithic forest cover, but their remains were all found alongside the remains of animals typical of fairly forested conditions, or at least of a mosaic of habitats ranging from forest to grassy woodlands. In other words, our early precursors of this period may have come to the ground, but they hadn’t yet abandoned the trees as their successors would ultimately do. INTHEBEGINNING The earliest of the putative early hominids is a form from Chad imposingly named Sahelanthropus tchadensis. Known principally from a skull and some other bits thought to be close to seven million years old, Sahelanthropus is a primate with a small (ape-sized) braincase but with a flattish face housing teeth that are not at all ape-like. In particular, the canines seem relatively reduced so that they do not project much beyond the level of the other teeth, and the upper canine does not sharpen itself on the lower premolar behind. What’s more, the molar teeth are squarish, and, in contrast to those of apes, they are coated with quite thick enamel, usually taken as a sign that relatively tough foods (maybe the tubers of plants that typically grew in more open areas) were being chewed, in contrast to the soft forest fruits favored by ancestral apes. Over the years much has been made of the significance of canine reduction—it has been putatively associated, for example, with changes in social organization, possibly in the direction of pair-bonding between males and females, making the reproductive unit a single adult couple. And once you have made that association, it doesn’t take much to imagine bipedal males foraging far and wide and filling their arms with food that was transported back to females and infants, reinforcing the pair bond and allowing females to reproduce more frequently, with the rest being history. Well, maybe. But it’s a bit of a stretch, and it’s at least as plausible to conclude that canine reduction “unlocked” the lower from the upper jaw, allowing side-to-side grinding of those tougher foodstuffs. As for bipedality, the single known skull of Sahelanthropus is crushed but sports a foramen magnum (the large hole through which the spinal cord exits the brain) that lies somewhat...

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